Electrical Testing Sequence

To comply with electrical safety standards under law, inspection and testing procedures should be performed on all non-domestic electrical installations. The electrical testing sequence will be determined primarily by whether testing is for initial verification of a new installation or periodic testing of an existing appliance.

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Initial Verification Testing Sequence

New installations and alterations require ‘Initial Verification’. This involves a specific electrical testing sequence to be followed. Each test builds on the previous one having passed, to give correct results without the test causing danger.

Dead testing
Electrical supply disconnected
Continuity of protective conductors including main and supplementary equipotential bonding
Continuity of ring final circuit conductors
Insulation resistance
D Protection by SELV, PELV or electrical separation
Basic protection by a barrier or enclosure provided during erection
Insulation resistance/impedance of floors and walls
Earth electrode resistance
Live testing
Electrical supply re-connected
Protection by automatic disconnection of the supply
J Earth fault loop impedance
K Additional protection
Prospective fault current
Check of phase sequence
Functional testing
Verification of voltage drop


Under BS 7671, reg. 612.1, tests A to G are, where relevant, to be carried out first and in order before the installation is energised:

  • Earthing and bonding satisfactory
  • All conductors present and continuous
  • Insulation satisfactory
  • No short circuits or excessive leakage
  • Polarity/connection of all items correct
  • Resistance of any earth electrodes sufficiently low

Insulation resistance test should be the last test done, and all equipment covers should be replaced, save for the cover of the distribution board, prior to re-energising.

Under regulation 612.1, tests I to O do not necessarily have to be conducted in a particular order, but IEE Guidance Note 3 stipulates all the tests to be conducted in the order above.

Following this order should in most cases help to ensure satisfactory results in one test will normally indicate that the following test can be carried out effectively, minimising the amount of retesting. In practice, however, the order may need to be varied for example to minimise disruption.

An experienced and qualified electrician will be able to assess and advise on the most appropriate testing sequence.

Periodic Inspection Reports Testing Sequence

A regular programme of testing and inspection is required to comply with current legislation. A periodic inspection may also be required to ensure a newly-acquired installation is safe.

A visual inspection of the entire electrical installation should first be performed to verify:

  • The installation complies with British Standards.
  • The installation is not damaged or deteriorated so as to impair safety.
  • The installation has been correctly selected and erected for the environment where it’s located and the installation meets current working practices.

Where appropriate, such as where a fault or risk of failure is identified, steps must be taken to inspect the affected circuits urgently and ascertain the safety of electrical installation:

  • Continuity – to ascertain that the earthing is continuous throughout the circuit.
  • Bonding Conductors Continuity – to ensure bonding is in place and effective.
  • Ring Circuit Continuity – ascertains whether or not the ring is complete.
  • Insulation Resistance – to test whether there has been any breakdown in insulation to the installation.
  • Polarity – to check that the installation is correctly wired.
  • Earth Fault Loop Impedance – to ascertain the Zs of the installation.
  • Earth Electrode Resistance – applies to TT systems only, to test the earthing rods.
  • RCD testing – to check that Residual Current Device disconnects the supply in the event of a fault.
  • Functional testing of isolators and breakers – to ensure that they disconnect the supply.

Importantly, there is no stipulated sequence of testing for periodic inspections. An assessment should be made by the engineer undertaking the test to determine the most appropriate, efficient and safest sequence of testing. In practical terms, this includes consideration of the nature of the problem, the type and location of the equipment, the environment, as well as taking into account mitigating cost and minimising operational disruption.

A Periodic Inspection Report is issued following a periodic testing exercise, to include a Schedule of Inspection and Schedule of Test Results and guidance information.

While the frequency of testing is determined by factors such as the equipment, the environment and the results of previous checks, standards and sequence for electrical testing procedures need to be followed correctly to ensure effectiveness of the exercise.

Do you have a question about electrical testing sequence?

Electrical safety is a mandatory requirement. Effective use of electrical testing procedures and following the relevant and appropriate testing sequence can ensure compliance and safety, with minimal disruption and cost to your operations. For help with your electrical testing, contact Emelec’s team of experienced electrical engineers.


This article is for informational purposes only and does not constitute direct advice.